Rollers or rubber blankets of this kind for printing presses are used in offset printing, for example. In this context, the printing agent, e.g. a customary printing ink, is transferred from a reservoir, via an inking unit to a printing plate, to which the respective image is applied, generally by a photomechanical process. The printing areas of the printing plate accept the ink, such that the image to be printed can be transferred to a rubber blanket that is likewise mounted on a cylinder. The printing ink is transferred from the rubber blanket to the respective print carrier, i.e. the material to be printed, such as a paper web, a film, or some other object. At the same time, the printing plate is wetted with a damping solution, which is supplied from a reservoir by a damping unit. The damping solution covers the non-printing areas of the printing plate, such that they do not accept ink, thereby producing the print image. The damping solution is usually water, which can contain alcohols or other additives. In this context, the damping unit and the inking unit each consist of a plurality of rollers, where, in some cases, rollers with an elastomeric covering work against rollers with a metallic, ceramic or plastic surface in order to homogenize the printing agent and the damping solution in the gap between the rollers (nip), prepare them in a uniform layer and ultimately apply them to the printing plate and the rubber blanket.
The rollers with an elastomeric covering have to satisfy a host of requirements, particularly demonstrating defined mechanical properties, such as hardness, wettability with the printing agent or the damping solution, mechanical and chemical resistance, abrasion resistance, good cleanability and the like.
Moreover, particular problems are posed by defined transfer of ink and damping solution from the respective ink and damping solution reservoir, via the respective inking and damping unit to the impression cylinder. For example, it has become apparent that there is occasionally no defined transfer of damping solution and/or printing agent to the impression cylinder, and thus ultimately to the blanket cylinder, this being referred to as “overemulsification” of the ink/damping solution emulsion, i.e. too much damping solution, particularly water, is incorporated into the printing agent. The consequence of this is that, on both the impression cylinder and the rubber blanket, the areas covered with ink and the areas covered with damping solution are ultimately not accurately separated from each other, and thus that unsharp contours, streaks, or other such phenomena impairing the print quality, occur on the printed print carrier, e.g. a paper web. This “overemulsification” is partly attributed to fluctuating process conditions during the printing process, also including climate or temperature fluctuations in the print unit, for example, although these are difficult to determine and reproduce in terms of their process parameters. There is consequently a need to improve the print quality and enable a printing result that remains very constant over time.
Furthermore, known rollers variously display disadvantages in terms of their back-transfer properties, i.e. the printing agent is not optimally transferred to the next roller in the nip, but carried back on the roller. This ultimately leads to undesirable distribution of the ink and can also result in undesirable transfer of ink into the damping unit. Moreover, in the event of a color change, some of the original ink can be taken up by the roller or the rubber blanket and transferred to the subsequent print unit, this possibly leading to undesirable color deviations. These problems have likewise not yet been satisfactorily resolved. An additional aim is to further improve the back-transfer properties of the rollers.
Moreover, starting from rollers with auxiliaries, such as fluorinated polyolefins, incorporated in the elastomeric roller covering, it is desirable to further improve the long-term stability of the roller, and thus the service life of the printing press and the maintenance effort involved.
Furthermore, consideration must be given to the fact that rollers and rubber blankets with an elastomeric covering are subject to wear in printing presses, this leading to a change in the surface properties of the roller or the rubber blanket, e.g. to a roughness that changes in the course of long periods of time, and changing wetting properties in relation to the printing agent and the damping solution. As a result, it becomes necessary to replace the roller covering and fit the roller core with a new covering at certain intervals. This leads to machine downtimes and is also cost-intensive, since the covering has to be removed entirely and a complete, new roller covering built up.
The object of the invention is therefore to provide a damping solution and/or printing agent transfer device in the form of a roller or a rubber blanket for printing presses that solves the problems described above, particularly enables a virtually optimum printing result over long periods of time, even in the event of changing process conditions, such as climate or temperature fluctuations, particularly also in terms of color quality in multicolor printing, that demonstrates excellent back-transfer properties, displays a substantially longer service life with unchanged properties, particularly as regards hardness and wettability with damping solution and/or printing agent, and that permits simple restoration in the event of wear induced by operation.